Method and apparatus of flush pump feature for portable liquid purifying filter

ABSTRACT

A flush pump feature on a liquid purifying filter includes a segment of flexible tubing containing a small bulb pump is described. Two check valves are positioned upstream and downstream of the bulb pump which then terminates with a simple manually operated open/closed valve. The addition of this flush pump feature enables the filter unit to be easily purged of air at first use and also will make the filter easier to clean and maintain without the need to remove it from a hydration carrier. In addition, the flush bulb feature can also be used to perform a simple visual integrity test of filter while out in a remote location and also can be used to effectively remove bulk water from the filter for lighter storage when not in use which also minimizes freeze related damage when used in a cold environment.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. patent application Ser.No. 61/644,239, filed May 8, 2012, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present application is directed to portable filtration systems andmore particularly, to a flush pump feature that allows a number ofdifferent operating modes to be performed to ensure proper operation ofthe filtration system.

BACKGROUND

Liquid purifying filters, or in particular portable water filters usedto purify water for drinking purposes in a remote location, have been inuse for many years. In some cases, water purifying filters, such as anultrafilter or a microfilter, have been incorporated as an inline filterwith hydration packs containing a water bladder reservoir that iscarried on one's back. In other cases, water filters might be aseparately carried item whereby one dips or attaches the inlet of thewater filter directly to a source of water to be purified.

In the situations described above, the filter must typically be primedto purge out air of a new filter before it can be effectively used. Insome cases, a special air permeable membrane might be used as an aid tohelp air removal at first use, however these membranes can be costly andadd complexity to the finished device. Also, use of an air permeablemembrane to aid air removal during actual use makes it difficult to testfilter integrity during manufacturing and when in use as many of thesemethods involve pressurized air to detect filter leaks. In other cases avent port is included on the water filter such that it can be opened topurge air out of the upstream compartment then closed in order tooperate the filter unit. This however, requires the inlet water feedingthe filter to be under a positive pressure in order to push air out ofthe vent port of the filter. For inline filter configurations, one mightneed to somehow squeeze the water bladder or hydration pack toaccomplish this task. This, however, generally requires the hydrationpack to be removed from the person's back such that they can applypressure to the pack, such as by sitting on the pack after opening thevent port. This can be cumbersome to the operator to perform. Forstand-alone filters whereby the inlet port of the filter may be placeddirectly into a stream or lake source, one cannot simply increase thehydrostatic pressure of the inlet water and thus making it verydifficult to prime and/or purge air out of the filter which cansignificantly reduce the flow rate through the filter. In these filtersystems, it is common to use suction pressure created by the operatorwho attempts to suck water from the purified outlet side of the filter.

Also, once a portable filter is in use in the field, sediment and/orother particulate can accumulate on the upstream compartment of thefilter which can lead to a plugging of the filter membrane and an a lossof filter flow performance. In these instances, current portable waterpurifier systems need to be cleaned repeatedly as part of routinemaintenance procedures to keep it functioning as intended. In order tocarry out these cleaning procedure, typically one must remove ordisconnect the filter from the hydration pack or inlet source and thenblow air into the purified outlet port of the filter which pushes theresident purified water backwards across the filter membrane as a meansto purge out the accumulated particulate in the upstream compartment ofthe filter. For these cases, the purged fluid would need to exit out ofthe filter inlet ports. If, however, the filter is designed with a ventport on the filter housing as a means to provide a second port to purgeout the accumulated particulate, one would need to open up the hydrationpack to access this vent port and then orientate the pack in a suitableway during the blow back operation such that the purged fluid can exitto the external environment instead of flowing into the internal spacebetween the bladder reservoir and the outer hydration carrier pack. Itcan be seen that these are highly manipulative operations to perform.

There is therefore a need to provide a system that overcomes the abovedeficiencies.

SUMMARY

To overcome the above difficulties associated with conventional systems,a flush pump feature on a liquid purifying filter is disclosed. In oneembodiment, a flush pump feature including a segment of flexible tubingcontaining a small bulb pump is described. In this embodiment, two checkvalves are positioned upstream and downstream of the bulb pump whichthen terminates with a simple manually operated open/closed valve. Itwill become apparent that the addition of this flush pump feature willenable the filter unit to be easily purged of air at first use and alsowill make the filter easier to clean and maintain without the need toremove it from the hydration carrier. In addition, the flush bulbfeature can also be used to perform a simple visual integrity test offilter while out in a remote location and also can be used toeffectively remove bulk water from the filter for lighter storage whennot in use which also minimizes freeze related damage when used in acold environment.

In a second embodiment of the invention is shown whereby the upstreamcheck valve is positioned at or near the inlet port of the purifyingfilter. In this configuration, the bulb pump unit feature can be used aspump feature to drive water through the filter without suction. Also, itcan be used in a pump assist mode whereby one simultaneously pumps thebulb unit and sucks water through the filter as a means to maximize therate of purified water being produced by the system.

In a third embodiment, the header caps of the filter are made of aflexible material such that the domed section of the cap can functionthe same as the bulb pump unit described in the second embodiment.

BRIEF DESCRIPTION OF DRAWING FIGURES

FIG. 1 is a side perspective view of a filtration system in accordancewith one embodiment;

FIG. 2 is a side perspective view of a filtration system in accordancewith one embodiment;

FIG. 3 is a side perspective view of a filtration system in accordancewith one embodiment;

FIG. 4 is side view of a filtration system in accordance with thepresent invention incorporated into a portable hydration pack that canbe worn by a person;

FIG. 5A shows a bulb pump unit of the present invention in a collapsedstate indicative of the filter unit passing an integrity test;

FIG. 5B shows the bulb pump unit of the present invention in an inflatedstate indicative of a damaged condition with respect to the filter unitresulting in failure of the integrity test; and

FIG. 6 is a cross-sectional view of one exemplary filtration device thatis part of the filtration system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with one embodiment of the present invention, a filtrationsystem is provided and includes a filter unit 100. The filter unit(device) 100 is in the form of a suitable filtration device thatprovides filtration and achieves the objectives of the presentinvention. Any number of different filter units 100 can be used in thepractice of the present invention.

The illustrated filter unit 100 includes an inlet port 110 for receivingan un-purified liquid, such as water or any other liquid, and an outletport 120 for delivering the purified liquid after passing through thefilter unit 100. The filter unit 100 is an elongated structure and theinlet port 110 and outlet port 120 are at opposite ends of the elongatedstructure; however, the ports can be located at different locations ofthe cartridge in a different embodiment. The filter unit 100 is thusdefined by a housing and it can take any number of different shapesincluding a cylinder as shown in the figures.

The filter unit 100 contains a filter element (filter means) (not shown)which can include a set or bundle of semi-permeable hollow fibermembranes that are potted at each end of the hollow fibers such asdescribed in the present applicant's previous patents including but notlimited to U.S. Pat. No. 6,719,907, issued Apr. 13, 2004 and U.S. Pat.No. 7,534,349, issued May 19, 2009, each of which is hereby incorporatedby reference in its entirety. The hollow fibers are elongated fibersthat have inner lumens through which liquid can pass and the fibers canbe bundled together within the cartridge.

Reference is made to FIG. 6, which schematically illustrates across-sectional view of one exemplary filtration cartridge 1000 inaccordance with one embodiment. Cartridge 1000 includes a housing 1002having a first end 1003 and an opposite second end 1005. Housing 1002 ispreferably cylindrical in shape and is formed of a rigid plasticmaterial. Housing 1002 contains a longitudinal bundle of semi-permeablehollow fibers 1008 that are arranged along the length of the housing1002. The semi-permeable hollow fibers 1008 serve as a means fortransferring the toxins or the like (foreign material), which are beingremoved, from the liquid flowing through the inner lumen portions of thefibers 1008. In particular, filtration occurs when the liquid isfiltered across the fiber's wall (e.g., the liquid flows from the innerlumen across the fiber wall to the exterior of the fiber). Thefiltration thus occurs by conduction of the liquid across thesemi-permeable hollow fibers. Any number of semi-permeable hollow fibers1008 that are commercially available for this intended purpose may beused. For example, semi-permeable hollow fibers 1008 come in variety ofdimensions and can be formed of polymers, such as polysulfone, or becellulose-based. It will be appreciated that there is a space 1009 thatis formed within the cartridge and external to the hollow fibers 1008.As described below, it is within this space 1009 that the filtered(purified) liquid is collected after having been filtered by beingconducted across the hollow fibers 1008.

The cartridge can include end caps 1020, 1030, at the first and secondends 1003, 1005, respectively. The inlet 110 can be integral to the cap1020 and the outlet 120 can be integral to the cap 1030. Between the endcap 1020 and the first ends of the hollow fibers 1008, a first headerspace 1021 is formed and similarly, between the second ends of thehollow fibers 1008 and the second end cap 1030, a second header space1031 is formed. As described below, these empty spaces 1021, 1031 allowfluid flow and can receive fluid from either external to the cartridgeor from the fibers 1008.

It will be appreciated that potting compounds are used to define the twoend header spaces 1021, 1031. In particular, at the first end 1003 ofthe cartridge a first potting compound 1040 that is used to form a sealaround the outside surfaces of the hollow fibers 1008. At the first end1003, the inner lumens of the fibers 1008 are completely open andtherefore, liquid is free to flow directly into the inner lumens of thehollow fibers 1008. Similarly, at the at the second end 1005 of thecartridge a second potting compound 1050 that is used to form a sealaround the outside surfaces of the hollow fibers 1008. At the second end1005, the inner lumens of the fibers 1008 are completely open andtherefore, liquid is free to flow out of the hollow fibers 1008 and intothe second header space 1031. It will be appreciated and will be moreclear from the below discussion that liquid contained within the secondheader space 1031 is, in a number of operating modes, unpurified(unfiltered) liquid that has flowed longitudinally within the innerlumens of the hollow fibers 1008 from one end to the other end.

The outlet 120 is not in direct fluid communication with the secondheader space 1031. Instead, the outlet 120 is in direct fluidcommunication with the external space 1009 that is defined within thecartridge housing outside of (external to) the hollow fibers 1008. Theoutlet 120 is constructed such that a conduit (flow path) 121 is definedfrom the external space 1009 to the outlet nozzle (port) 120 thatextends beyond the cartridge housing. The conduit 121 thus fluidly linksthe external space 1009 to the outlet nozzle; however, the conduit 121is routed outside of the second potting compound 1050 so as to avoidbeing in communication with the second header space 1031. Since thespace 1009 contains purified liquid, the outlet 120 receives fluid fromthis location and more specifically, the outlet 120 is illustrated atthe second end of the cartridge as an exemplary location for the outlet120; however, the outlet 120 can be formed at other locations such asalong the side of the cartridge. In such a location, the outlet 120 isin the form of a nozzle (port) that is in direct communication with thespace 1009 to allow filtered liquid to flow from the space 1009 out ofthe cartridge (in purified form) and thus, be available for drinking oruse.

It will be appreciated that the present invention is not intended tocover the specifics around the filter element and/or filter unit design(and thus is not limited to the constructions shown in FIG. 6) butrather is directed to an added feature that makes the use of theportable filter unit more easy to use in the field (e.g., outdoor). Inorder to be used in the filtration scheme disclosed herein, the filterunit 100 is constructed so as to at least contain the inlet port 110 forreceiving unpurified liquid, the outlet port 120 for delivery of thepurified liquid, and a flush port 130 that is in fluid communicationwith an upstream compartment of the filter unit 100 whereby air and/oraccumulated sediment can be purged out of the upstream compartment, suchas during priming and cleaning operations as disclosed herein.

A flush pump feature 200 is composed of a tubing segment 210, twoone-way flow check valves 220, 230, a flexible bulb unit 240, and aflush valve 250, whereby the internal fluid path of the flush pumpcomponents is in fluid communication both with the upstream compartmentof the filter unit 100 and the flush port 130. The flush pump feature isthus in fluid communication with a region (upstream compartment) of thecartridge in which unpurified liquid exists (i.e., a location at whichthe liquid has not undergone the filtration process by being conductedacross the hollow fibers).

The tubing segment 210 can be a flexible tubing segment, such as madefrom a flexible PVC material while its length can be as short or as longas desired depending upon how the filter system is being used. Forexample, if the filter unit 100 is contained inside a hydration carrierpack (worn by a user), the length of the tubing segment 210 can beadjusted so as have the bulb unit 240 and the flush valve 250 easilyaccessible (e.g., by routing them to a position that is accessible onthe outside of the hydration pack).

It will be appreciated that the tubing segment 210 is in direct fluidcommunication with the second header space 1031 and thus, fluid exitingthe inner lumens of the hollow fibers 1008 can flow directly into thesecond header space 1031 and into the tubing segment 210 as describedbelow. As mentioned above, since the outlet 120 is not in communicationwith the second header space 1031, the tubing segment 210 is not influid communication with the outlet 120.

The check valves 220, 230 can be any of those known in the art, whichinclude but are not limited to flap valves, duck-billed type valves,disc valves, or ball and seat valves. The check valves 220, 230 thusallow fluid to flow in one direction, namely in a direction toward theflush port.

The bulb unit 240 can be a simple bulb pump type made from a flexiblematerial as known in the art, or can be made using another volumedisplacement pump configuration which can be operated manually such as abellows type pump that can contain an internal spring to keep it anexpanded state. The flush valve 250 can be a simple open/close typevalve with a lever used to operate the valve, or can simply be a capthat taken on or off to effectively open or close the flush ports.Operation of the filter unit 100 containing the flush pump feature 200is further described below. More specifically, the flush pump feature200 has a number of different operating conditions (modes) that aredescribed below.

For example, a first operating mode is a forward-flush/air-purge mode asdescribed below.

1) Forward-Flush/Air-Purge:

One exemplary operation of this mode is when the filter unit 100 isconnected with a hydration pack 10 (FIG. 4) to a reservoir that isfilled with a liquid (e.g., water) and a hydration drink tube valve 21(that is associated with a drink tube 20) is closed. FIG. 4 shows suchexemplary construction in which the hydration pack is generally shown at10 and the drink tube is generally shown at 20. The drink tube 20 isconnected at its end to the outlet 120 and thus purified liquid flowsthrough the drink tube 20 to the user for consumption/use. The drinktube valve 21 is located along the length of the drink tube 20 and asmentioned above, this valve is closed in this operating mode. Any numberof different controllable valves can be used for valve 21.

To perform a forward-flush and/or air-purge of the filter unit 100, theflush port valve 250 is first opened, thereby providing communicationwith the second header space 1031 and the inner lumens of the fibers1008. Next, the bulb pump unit 240 is squeezed until a clear and steadystream of fluid (e.g., water) without any air bubbles is observedexiting the flush valve 250. This results since operation of the bulbpump unit 240 creates negative pressure which causes fluid within thesecond header space 1031 and within the inner lumens of the hollowfibers 1008 to be drawn into the tubing (conduit) 210 before exitingthrough open flush valve 250 as described below.

In one embodiment, at least about ½ cup exits the flush valve 250;however, in other embodiments, a different volume can be dischargedduring performance of this step.

Thus, upon squeezing the bulb pump unit 240, fluid is pushed out of thebulb pump unit 240 through the outlet check valve 230, while the inletcheck valve 220 prevents fluid from going back into the filter unit 100.After squeezing the bulb pump unit 240, the bulb pump unit 240 isallowed to relax back to its normal state by removing one's grip of thebulb pump unit 240. This creates a negative pressure inside the bulbpump unit 240 which draws fluid through the inlet check valve 220 andinto the bulb pump unit 240. This effectively draws additionalunpurified water into the inlet port 110 and the upstream compartment(including first header space 1021) of the filter unit 100. Theorientation of the outlet check valve 230 prevents fluid from comingback toward the bulb pump unit 240 from the flush port side. Repeatedpumping of the bulb pump unit 240 draws a semi-continuous stream ofun-purified fluid through the upstream compartment of the filter unit100 to forward flush contents out through the flush port 130. At thecompletion of this step, the flush port valve 250 is closed so as toready the unit 100 for use. If water is being purified by the filterunit 100, the drink tube valve is opened and a user can drink thepurified water through the drink tube 20.

It will be appreciated that when the flush valve 250 is closed, thesecond header space 1031 is effectively closed off and liquid does notflow through the inner lumens of the hollow fibers to the second headerspace 1031 (since water already fills this compartment and has nowhereto flow). Instead, water (liquid) is forced across the semi-permeablehollow fibers 1008, thereby filtering the liquid. Thus, operation of thefilter unit 100 results in filtering of the liquid.

A second operating mode is one in which the filter unit 100 is cleanedwith combination of back-flush and forward-flush.

2) Cleaning the Filter with Combination Back-Flush and Forward-Flush:

In the case of very dirty (turbid) liquid (water), a user can perform acombination back-flush and a forward-flush to more thoroughly clean thefilter unit 100 as described below.

First, the user makes sure that the liquid (water) is contained insidethe drink tube 20 by sucking on the drink tube 20 until the liquid(water) is coming out (i.e., filtered liquid within space 1009 is drawnthrough outlet 120 and into the drink tube 20). Next, the user opens theflush valve 250 and manually blows air into drink tube 20 by mouth,while simultaneously squeezing the bulb pump unit 240 until the fluidstream is relatively clear or free of the concentrated sediment. Uponblowing air back into the drink tube 20, the water contained in thedrink tube 20 is effectively forced backward across the filter element(hollow fibers 1008) of the filter unit 100 to help dislodge particulatethat may be stuck to the dirty side of the filter element. In otherwords, the liquid flows across the hollow fibers 1008 from the exteriorspace 1009 to the inner lumens of the hollow fibers 1008.

As indicated in the immediately preceding operating mode, simultaneouspumping of the bulb unit 240 draws a semi-continuous stream ofun-purified fluid through the upstream compartment of the filter unit100 to forward flush contents out through the flush port 130. Whencompleted, the user then closes the flush valve 250 to ready the filterunit 100 for use.

Yet another operating mode is a mode for emptying the filter unit 100 ofbulk liquid.

3) To Empty Filter Unit of Bulk Liquid:

In order to fully remove excess liquid from the filter unit 100, a usercan perform the following steps.

First, a user opens the flush valve 250 and pumps the bulb pump unit 240until the exiting stream is relatively clear and without air bubbles.Next, the user disconnects the inlet filter port 110 from the inletsource (in this example the reservoir bladder contained in the hydrationpack 10) and immediately caps the inlet filter port 110 to prevent fluidfrom entering or exiting the inlet filter port 110. Next, the user makessure that the filter outlet port 120 is open to atmospheric pressure.The user then pumps the bulb pump unit 240 until water flow ceases tocome out of the flush port 130. Because the inlet port 110 is capped,fluid is drawn backwards across the filter element (hollow fibers 1008)upon repeated pumping of the bulb pump unit 240. In other words, theliquid flows from exterior space 1009 to the inner lumens of the hollowfibers 1008. When all the fluid is drawn across the filter element(conducted across the hollow fibers 1008), the bulb pump unit 240 willremain in a flat position (i.e., no longer is able to expand back to itsnormal shape).

At this point, the downstream filter compartment (including secondheader space 1031) of the filter unit 100 should be filled with air thathas entered from the purified exit port 120. Next, while holding thefilter unit 100 upside-down, the user then removes the cap that wasplaced on the inlet port 110 which allows air to enter directly from theinlet port 110. Repeated pumping of the bulb pump unit 240 now draws asemi-continuous stream of air into the upstream compartment (firstheader space 1021) which further displaces the upstream liquid until nomore liquid comes out from the flush port 130. In other words, air drawninto the first header space 1021 displaces fluid within the inner lumensof the hollow fibers 1008.

If desired, the user can then shake the filter unit 100 to remove anyexcess fluid contained at or near the inlet or outlet ports 110, 120.Upon removal of the bulk liquid, the user can close the flush port valve250 and cap the inlet/outlet ports 110, 120 for storage of the filterunit 100.

In yet another operating mode, a field integrity test is performed asdescribed below.

4) Field Integrity Test (FIT)

To perform the field integrity test, the following steps are performedto check for damage of the filter unit 100 including the filter element(hollow fibers 1008).

First, the user opens the flush valve 250 and pumps the bulb pump unit240 (by squeezing the bulb) until the exiting stream is relatively clearand without air bubbles. Next, the user disconnects the inlet filterport 110 from the inlet source (in this example the reservoir bladdercontained in the hydration pack) and immediately caps the inlet filterport 110 to prevent fluid from entering or exiting the inlet filter port110. Next make sure that the filter outlet port 120 is open toatmospheric pressure. The user then pumps (by squeezing) the bulb pumpunit 240 until water flow ceases to come out of the flush port 130.Because the inlet filter port 110 is capped, fluid is drawn backwardsacross the filter element (fluid flows from exterior space 1009 to theinner lumens of the hollow fibers 1008) upon repeated pumping of thebulb pump unit 240. When all the fluid is drawn across the filterelement, the bulb unit should remain in a flat position (i.e. no longeris able to expand back to its normal shape) provided the filter unit 100including its filter element (hollow fibers 1008) is intact and providedthat an intact filter element does not normally allow air to passthrough. It is understood to those skilled in the art that air pressuretests (e.g., bubble point, air flow, and pressure decay tests) are usedto measure filter integrity which includes the filter element inside thefilter unit. Upon visual inspection of the flattened bulb pump unit 240over a set period of time, such as 10 to 40 seconds, one can determineif the filter unit 100, including its filter element, has failed or not.As an example, FIGS. 5A and 5B show the appearance of the bulb pump unit240 after a set period of time as elapsed once it reached the flattened(or collapsed) state. FIG. 5A shows the bulb pump unit 240 remainingflat (compressed) for at least 40 seconds indicating the filter is good(no significant damage). However, if the bulb pump unit 240 does notstay compressed, such as in FIG. 5B, the filter integrity may have beencompromised. In other words, if the filter element is damaged, such ashaving a hole, air can flow into the fiber(s) and then flows to the bulbpump unit 240 resulting in inflation of the bulb. Depending upon itsuse, the user can then take proper precautions on whether or not to usethe filter after the test has been performed.

In a second embodiment of the invention, the inlet check-valve to thebulb pump unit 240 has been repositioned to add additional functionalityof the flush pump feature 200. As shown in FIG. 2, a first check-valve270 is positioned at or near the inlet port 110 of the filter unit,while the second check-valve 230 remains at the distal end of the bulbpump unit 240. The advantage of this is that it enables a pump and/orpump assist mode of the filter unit which is further described below.

Additional operating modes include pump and pump-assist modes.

5) Pump and Pump-Assist Modes:

This is similar to the operating mode described above in which thefilter unit 100 is connected with a hydration pack containing areservoir filled with liquid (water) and the hydration drink tube valveis closed as shown in the FIG. 4.

After the filter unit 100 has been primed and is ready for use (flushvalve 250 closed) in a similar manner as described above, the user opensthe drink tube valve such that it is open to atmospheric pressure. Nowupon repeated squeezing of the bulb pump unit 240, a positive pressureis created on the fluid residing in the upstream compartment of thefilter unit 100. This is apparent since fluid contained in the bulb pumpunit 240 cannot exit through the closed flush valve 250 and cannot exitout through the inlet filter port 110 because of the positioned checkvalve 270 at this location. Since the outlet port 120 is open toatmospheric pressure, the higher pressure caused by squeezing the bulbpump unit 240 is sufficient to force water across the filter element andout through the outlet port 120 thus creating purified fluid. Uponrelease of the bulb pump unit 240, the bulb returns to its normal(extended) state which creates a negative pressure within the upstreamcompartment of the filter unit 100. Provided un-purified fluid can moreeasily enter the inlet port through check-valve 270 than can be reversefiltered from the “just-purified” fluid in the downstream compartment ofthe filter unit 100, the upstream compartment will fill mostly withun-purified fluid. In this way, there is a net forward movement ofun-purified fluid (water) across the filter element 1008 and out thepurified exit port 120. In this mode, the bulb pump unit 240 acts as apositive displacement pump which enables purification without the needto manually suck fluid through the filter using the drink tube.

In a pump-assist mode, the same method used above can be used with theaddition that the user can also simultaneously drink (suck) water fromthe drink tube 20. In this mode, pone can drink water at a higher ratethan by sucking alone.

In a third embodiment, as illustrated in FIG. 3, the end caps 101, 102of the filter unit 100 can be constructed with a flexible material suchas silicone rubber or flexible PVC or may have a flexible domed insertas part of the end cap. To those skilled in the art, one can see that itwould be possible to integrate the function of the bulb pump unit aspart of this flexible domed header cap. As shown in FIG. 3, end cap 102contains a flexible domed feature 280 that can be manually pushed inwardto depress the dome and released to allow the dome to return back to itsnormal shape. This action would have the same result as pumping the bulbpump unit 240 described in the second embodiment which is discussed asfollows. Upon repeated pressing of the domed portion 280, a positivepressure is created on the fluid residing in the upstream compartment ofthe filter unit 100. This is apparent since fluid contained in the domedregion of the end cap 102 cannot exit through the closed flush valve 250and cannot exit out through the inlet filter port 110 because of thepositioned check valve 270 at this location. Since the outlet port 120is open to atmospheric pressure, the higher pressure caused bydepressing the domed end cap 102 is sufficient to force water across thefilter element and out through the outlet port thus creating purifiedfluid. Upon release of the domed end cap, the dome feature returns toits normal state which creates a negative pressure within the upstreamcompartment of the filter unit. Unpurified fluid then enters the inletport through check-valve 270 to refill the upstream compartment. In amanner similar to the second embodiment described herein, one canoperate the system in both a pump mode or in a pump-assist mode.

It will be understood that the above disclosure is merely exemplary andis not limiting of the scope of the present invention which coversvariations thereof.

What is claimed is:
 1. A portable liquid purifying device configured to purify a source of liquid in a remote location comprising: a filtration unit defined by a housing that contains a filter element for filtering a liquid, the filtration unit having an inlet for receiving unpurified liquid and an outlet for discharging purified liquid that has passed through the filter element, wherein a first header space is formed between a first end of housing and a first end of the filter element and a second header space is formed between a second end of the housing and a second end of the filter element, wherein an interior space is defined between the housing and an exterior of the filter element, the interior space being prevented from having fluid communication with an interior of the filter element in which the unpurified liquid flows, wherein the inlet is in fluid communication with the first header space and the outlet is in fluid communication with the interior space and not the second header space; a flush pump accessory that is coupled to the filtration unit and configured to operate according to a plurality of different operating modes, the flush pump accessory having a first conduit that is in fluid communication with the second header space; a bulb pump that is fluidly connected at a first end to the first conduit; a flush valve that is disposed along a second conduit that is fluidly connected to a second end of the bulb pump, wherein in a closed position, the flush valve prevents liquid to flow through the second conduit to a flush port; and a plurality of valve members including: a first valve that is located between the bulb pump and the inlet so as to be upstream of the bulb pump, the first valve configured to restrict flow of the unpurified liquid out of the inlet of the filtration unit when in a closed position; and a second valve disposed between the bulb pump and the flush port, wherein the first valve, second valve and flush valves are open when at least one of a flush operation and air purge operation is performed and at least the second valve and the flush valve are closed during a filtration operation in which unpurified liquid is filtered across the filtering element to the internal space and then flows through the outlet as purified liquid.
 2. The device of claim 1, wherein the first valve is located within the first conduit.
 3. The device of claim 1, wherein the first valve is located within the inlet upstream of the first header space.
 4. The device of claim 1, wherein the first and second valves comprise one way check valves that only allow liquid to flow in a direction toward the flush port.
 5. The device of claim 1, wherein the filtering element comprises a plurality of semi-permeable hollow fibers arranged longitudinally within the housing.
 6. The device of claim 5, wherein the plurality of semi-permeable hollow fibers comprises a bundle of fibers and the interior space is a space that surrounds the bundle and is formed adjacent and inner surface of the housing.
 7. The device of claim 1, further comprising a first potting compound that surrounds first ends of the semi-permeable hollow fibers and partially defines the first header space and a second potting compound that surrounds second ends of the semi-permeable hollow fibers and partially defines the second header space, the first ends of the semi-permeable hollow fibers being open to the first header space and the second ends of the semi-permeable hollow fibers being open to the second header space.
 8. The device of claim 7, wherein the outlet is fluidly connected to the interior space along a flow path that is outside of the second potting compound to allow purified liquid to flow from the interior space to the outlet without passing through the second potting compound.
 9. The device of claim 1, wherein the bulb pump comprises a compressible bulb that is configured to create a negative pressure when compressed to thereby cause unpurified liquid to flow into the second header space and be drawn into the first conduit.
 10. The device of claim 1, wherein the plurality of operating modes includes a field integrity test in which the integrity of the filtering element is tested, wherein a failure of the filtering element is represented by the bulb pump assuming an inflated condition after being collapsed and after passage of a predetermined period of time and wherein, integrity of the filtering element is confirmed when the bulb pump maintains a collapsed position after passage of the predetermined period of time.
 11. The device of claim 10, wherein during performance of the filter integrity test, the inlet is closed to prevent fluid from entering the first header space and the outlet is open to atmosphere.
 12. The device of claim 1, wherein the portable liquid purifying device is incorporated into a portable hydration pack that that has a reservoir that hold the source of liquid which comprises water and an elongated flexible drink tube is fluidly connected to the outlet, the drink tube having a valve to allow a user to control discharge of purified water from the drink tube.
 13. A method for performing a filter integrity test on a filter element associated with a portable filtration device comprising the steps of: fluidly connecting a flush pump accessory to the portable filtration device, wherein the portable filtration device includes: a housing in which the filter element is contained, an inlet for receiving unpurified liquid and an outlet for discharging purified liquid that has passed through the filter element, wherein a first header space is formed between a first end of housing and a first end of the filter element and a second header space is formed between a second end of the housing and a second end of the filter element, wherein an interior space is defined between the housing and an exterior of the filter element, the interior space being prevented from having fluid communication with an interior of the filter element in which the unpurified liquid flows, wherein the inlet is in fluid communication with the first header space and the outlet is in fluid communication with the interior space and not the second header space, wherein the flush pump accessory includes: a conduit that is in fluid communication with the second header space and includes a flush port at an open distal end thereof; a bulb pump that is fluidly connected to the conduit; a flush port valve that is disposed along the conduit to control flow of the unpurified liquid through the conduit to the flush port; closing the inlet to prevent unpurified liquid from flowing into the first header space; opening the outlet to atmosphere; opening the flush port valve; repeatedly squeezing the bulb pump until liquid ceases to flow out of the flush port and the bulb of the bulb pump remains in a collapsed state; and visually inspecting the collapsed bulb pump over a predetermined period of time to determine if the filter unit, including the filter element thereof, has failed or not, wherein failure of the filter unit is identified by inflation of the bulb during the predetermined period of time, while integrity of filter unit is confirmed by the bulb remaining in the collapsed state.
 14. The method of claim 13, wherein the step of repeatedly squeezing the bulb pump causes liquid in the interior space to be drawn backwards across the filter element.
 15. The method of claim 13, wherein the filter elements comprises a plurality of semi-permeable hollow fibers that are arranged longitudinally within the housing, the semi-permeable hollow fibers being formed to prevent air flow thereacross into inner lumens thereof.
 16. The method of claim 13, wherein the predetermined period of time comprises a period of time less than 1 minute.
 17. The method of claim 16, wherein the predetermined period of time comprises a period of time between 10 seconds and 40 seconds.
 18. The method of claim 13, wherein prior to performing the filter integrity test, a forward flush operation is performed by: opening the flush port valve; and squeezing the bulb pump until a clear and steady stream of unpurified liquid without any bubbles is observed exiting the flush port.
 19. The method of claim 13, wherein prior to performing the filter integrity test, a combined back-flush and forward flush operation is performed to more thoroughly clean the filter element by: opening the flush port valve and blowing air into the outlet, while simultaneously squeezing the bulb pump until a fluid stream exiting the flush port is relatively clear or free of concentrated sediment.
 20. A portable liquid purifying device configured to purify a source of liquid in a remote location comprising: a filtration unit defined by a housing that contains a filter element for filtering a liquid, the filtration unit having an inlet for receiving unpurified liquid and an outlet for discharging purified liquid that has passed through the filter element and has been purified; a flush pump accessory that is coupled to the filtration unit and configured to operate according to a plurality of different operating modes, the flush pump accessory being connected to the filtration unit by a flush pump conduit and including a bulb pump that is disposed along the flush pump conduit and a flush valve that is disposed along the flush pump conduit, the flush valve being movable between an open position in which fluid can flow from the inlet of the filtration unit to an open end of the flush pump conduit and a closed position in which fluid is prevented from flowing out of the open end of the flush pump conduit, wherein the bulb pump is configured to draw unpurified liquid from the inlet of the filtration unit to the open end of the flush pump conduit; and a plurality of valve members including: a first valve that is located between the bulb pump and the inlet, the first valve configured to prevent backflow of the unpurified liquid out of the inlet of the filtration unit; and a second valve disposed between the bulb pump and the open second end of the flush pump conduit.
 21. The device of claim 20, wherein the first and second valves are one-way check valves.
 22. The device of claim 20, wherein the filtration unit includes a first header space that is in fluid communication with both the inlet and the filter element, a second header space that is in fluid communication with only the filter element and an external space that is located external to the filter element and in fluid communication with the outlet, wherein the external space is not in direct fluid communication with the outlet.
 23. The device of claim 22, wherein the filtering element comprises a plurality of semi-permeable hollow fibers arranged longitudinally within the housing and semi-permeable hollow fibers including open first ends in communication with the first header space and open second ends in communication the second header space, wherein the external space is not in direct fluid communication with the open first and second ends of the semi-permeable hollow fibers.
 24. The device of 22, wherein the flush pump conduit comprises flexible tubing and the outlet and second header space are located at the same end of the housing.
 25. The device of claim 23, wherein the open first and second ends of the semi-permeable hollow fibers are sealed from the external space that is disposed within a hollow interior of the housing. 